sporadic connection problems to specific websites

[ebuddington]

I have sporadic problems connecting to a couple of Dreamhost IPv6 websites through a couple of HE tunnels.
Specifically, large packets returning from Dreamhost's server don't make it, and the browser hangs, waiting for data. Here are two traces for comparison:

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Working:

08:52:07.378551 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags , seq 1545250714, win 14400, options [mss 1440,sackOK,TS val 6431801 ecr 0,nop,wscale 6], length 0
08:52:07.591154 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [S.], seq 1794918474, ack 1545250715, win 5760, options [mss 1440,nop,nop,sackOK], length 0
08:52:07.591228 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1, win 14400, length 0
08:52:07.592777 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags [P.], seq 1:241, ack 1, win 14400, length 240
08:52:07.830860 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [.], ack 241, win 6432, length 0
08:52:07.839053 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [.], seq 1:1381, ack 241, win 6432, length 1380
08:52:07.839095 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1381, win 16560, length 0
08:52:07.839205 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [P.], seq 1381:2025, ack 241, win 6432, length 644
08:52:07.839217 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 2025, win 19320, length 0
08:52:07.839276 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [F.], seq 2025, ack 241, win 6432, length 0
08:52:07.843634 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953 > 2607:f298:1:107::686:75d6.80: Flags [F.], seq 241, ack 2026, win 19320, length 0
08:52:07.998149 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55953: Flags [.], ack 242, win 6432, length 0
08:52:09.699218 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.55910: Flags [.], seq 786191541:786192921, ack 594113516, win 6432, length 1380
08:52:09.699276 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.55910 > 2607:f298:1:107::686:75d6.80: Flags [R], seq 594113516, win 0, length 0

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Not working (web browser hangs waiting for data):

09:05:47.247850 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags , seq 1132179152, win 14400, options [mss 1440,sackOK,TS val 6636768 ecr 0,nop,wscale 6], length 0
09:05:47.370508 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038: Flags [S.], seq 1287332309, ack 1132179153, win 5760, options [mss 1440,nop,nop,sackOK], length 0
09:05:47.370586 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1, win 14400, length 0
09:05:47.373614 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags [P.], seq 1:241, ack 1, win 14400, length 240
09:05:47.502780 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038: Flags [.], ack 241, win 6432, length 0
09:05:47.506488 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038: Flags [P.], seq 1441:2025, ack 241, win 6432, length 584
09:05:47.506553 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1, win 14400, options [nop,nop,sack 1 {1441:2025}], length 0
09:05:47.506624 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038: Flags [F.], seq 2025, ack 241, win 6432, length 0
09:05:47.506644 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1, win 14400, options [nop,nop,sack 1 {1441:2026}], length 0
09:05:47.670170 IP6 2607:f298:1:107::686:75d6.80 > 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038: Flags [.], seq 1421:1441, ack 241, win 6432, length 20
09:05:47.670235 IP6 2001:470:8d44:2:214:a5ff:fe5c:72f6.49038 > 2607:f298:1:107::686:75d6.80: Flags [.], ack 1, win 14400, options [nop,nop,sack 1 {1421:2026}], length 0

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The browsing computer is on a LAN of MTU 1500. The tunnel, however, has a MTU of 1472. I expect PMTUD to handle this transparently, but I think that's what's failing.

Can I assume that the other end of my HE tunnel sends back appropriate ICMP errors for oversize packets?